The present invention relates generally to a tractor for use in delivering continuous paper in a printing device, such as a printer or the like, and also to a continuous paper feed mechanism using such a tractor. In particular, the present invention relates to a tractor capable of conveying, both in the forward and in the reverse direction, continuous paper when the width thereof varies due to a change in temperature or humidity. The present invention also relates to a continuous paper feed mechanism using such a tractor.
Generally, a tractor which includes an endless pin belt with arrays of pins thereon is constructed and arranged so that holes formed on the two sides of the continuous paper engage the pins of the pin belt to feed the continuous paper. If the width of the continuous paper increases or decreases due to a change in temperature or humidity when the position of the tractor (that is, the pin belt) is fixed, the holes of the continuous paper cannot properly engage the pins of the tractor, resulting in an inability to properly feed the continuous paper.
Japanese Patent Laid-Open Publication No. 1-271344 (Heisei) describes a proposed tractor that attempts to solve the heretofore mentioned problem. FIG. 9 depicts a plan view of the tractor described in Japanese Patent Laid-Open Publication No. 1-271344 (Heisei).
Shown in FIG. 9 is a drive shaft 1, a guide shaft 2 and a frame member 3 which is slidably mounted onto drive shaft 1 and guide shaft 2. A tractor 4 is positioned within frame member 3 and is slidably mounted onto drive shaft 1 and guide shaft 2. Tractor 4 is forced in the direction of arrow X1, as shown in FIG. 9, by a spring 5 interposed between frame member 3 and tractor 4. Holes 6a are respectively formed on the two side portions of continuous paper 6. Tractor 4 also includes a pin belt, with a plurality of pins 4a disposed thereon. Pins 4a are aligned and meshed with holes 6a to convey continuous paper 6 in a sheet feeding direction. A cover plate 4b is provided for guiding continuous paper 6 and loosely holding the side portion 6b of continuous paper 6 between the pin belt and cover plate 4b. Cover plate 4b has an elongated hole 4c formed therein that allows pins 4a to extend therethrough. A lock mechanism 7 selectively secures frame member 3 to guide shaft 2, so that frame member 3 can be prevented from sliding.
Although FIG. 9 depicts only the left tractor, the right tractor is identical to the tractor of FIG. 9 except to the extent that the right tractor does not include frame member 3 and spring 5. The right tractor is also fixed to guide shaft 2.
In this arrangement, spring 5 constantly applies tension to continuous paper 6, causing tautness in continuous paper 6 in the widthwise direction. Therefore, even if the width W of continuous paper 6 increases or decreases due to a change in temperature or humidity, the increase or decrease is compensated by the sliding of tractor 4 along drive shaft 1 and guide shaft 2 and the two side edge portions 6b of continuous paper 6 are kept parallel to each other. In this manner, continuous paper 6 can be conveyed in the forward or reverse direction.
The conventional tractor employing the structure described above has the following problem. When the width W of the continuous paper increases or decreases while the two sides edge portions 6b of continuous paper 6 remain parallel to each other, the paper increase or decrease in the widthwise direction is compensated by sliding tractor 4 horizontally so that continuous paper 6 can be properly conveyed. However, in some instances, the width of the continuous paper does not uniformly increase or decrease in such a manner that the two side edge portions 6b remain parallel, but rather, the side edge portions 6b vary in such a way that the continuous paper, when viewed lengthwise, appears to taper.
Although the conventional tractor will slide, the tractor cannot accurately follow the variations in the paper when the two side edge portions of the continuous paper taper. As a result, holes 6a of continuous paper 6 may shift, causing a misalignment between at least one pin 4a and at least one hole 6a, resulting in unreliable paper conveying, regardless of whether it is in a forward or reverse direction.
The variation in width of the continuous paper may be caused by a change in the temperature or humidity. Most frequently, the change will occur because of the frequent changes in temperature or humidity during the course of an average day, week, etc. where the printer is operating. A change may also occur when the continuous paper supply is transported from one environment with a set temperature and/or humidity to another environment having a different temperature and/or humidity. As will be explained below, because different portions of the paper are exposed to different amounts of the outside air, the paper, throughout a predetermined length, may vary in width by a relatively large amount.
Reference is now made to FIGS. 10(a), (b) and FIG. 11 to more specifically illustrate the effect of having different portions of the continuous paper exposed to different temperature and/or humidity conditions.
As illustrated in FIG. 10(a), alignment is typically made between a front end 6c of continuous paper 6 and the conventional tractor of a conventional printing apparatus 8, while the remaining continuous paper portion 6d of continuous paper 6 remains in a corrugated cardboard box 9, placed by way of example, on the floor.
By way of example, an air conditioning unit may reduce the humidity within the room that houses printing apparatus 8. The portion of continuous paper 6 between printing apparatus 8 and corrugated cardboard box 9 which is exposed to the air has water being constantly evaporated therefrom, causing continuous paper 6 to decrease in the widthwise direction. However, the unused portion 6d of continuous paper 6, which remains in corrugated cardboard box 9, is essentially not exposed to the air, but for the end portion thereof. Accordingly, unused portion 6d will have more moisture therein than the exposed portion of continuous paper 6 and therefore may also be wider than the exposed portions of the continuous paper.
In other words, the width of continuous paper 6 proximate to printing apparatus 8 maybe narrower than the width of continuous paper 6 within corrugated cardboard box 9. Accordingly, as shown in FIG. 1t, the width of continuous paper 6 may vary in a tapered manner from a wide portion to a narrow portion.
As noted above, variations in the nature of the taper in the width of continuous paper can result when temperature and/or humidity varies between the place storing the continuous paper and the location of the continuous paper where the printing apparatus is ultimately located. Thus, for example, if continuous paper 6 is stored in an area having an essentially constant high temperature or humidity, in a warehouse for example, then continuous paper 6 will absorb a relatively large amount of water and the width of continuous paper 6 will increase. However, if the expanded continuous paper 6 is then used with printing apparatus 8 in an environment where the temperature and/or humidity is low, such as in an air conditioned facility, the portion of continuous paper 6 proximate to printing apparatus 8 will essentially immediately begin drying because of the evaporation of moisture. Accordingly, the width of continuous paper 6 will decrease. However, unused portion 6d of continuous paper 6 located within corrugated cardboard box 9 will not have moisture evaporate therefrom at the same rate as the portion proximate to printing apparatus 8 because only the end portion thereof is exposed to the air. Therefore, the width of the paper in corrugated box 9 will not decrease as rapidly or as much as the portion proximate to printing apparatus 8, and the width of continuous paper 6 proximate to printing apparatus 8 will not equal the paper width of continuous paper 6 within corrugated cardboard box 9. Again, FIG. 11 illustrates a sheet of continuous paper that varies in width. The paper width tapers from the wide portion to the narrow portion and, hence, does not feed properly.
When the width of continuous paper 6 varies in the tapered manner as described above, the conventional tractor cannot follow the width variations of continuous paper 6 and, as further shown in FIG. 11, one or more holes 6a of continuous paper 6 shift away from one or more pins 4a, which will result in poor paper conveying.
Accordingly, it is desired to provide an improved tractor having a construction which will allow continuous paper to be accurately fed even if the width of the continuous paper varies (either increases or decreases) in a tapered manner. It is also desired to provide an improved continuous paper feed mechanism having a construction which uses such an improved tractor construction.